feat: skip gitignore for external patterns

[koistya]

Summary

• External patterns (../) now skip .gitignore filtering since it only applies within cwd
• Adds isExternalPattern() helper to detect parent directory references
• Handles redundant ./ prefix (e.g., ./../other)

Example

// srcpack.config.ts
export default {
  bundles: {
    context: {
      include: [
        "src/**/*.ts",           // Respects .gitignore
        "../shared/utils/**/*",  // Skips .gitignore (external)
      ],
    },
  },
};

Test plan

• Unit tests for external pattern detection
• Tests verify gitignore is not applied to external paths